1. Field of the Invention
The present invention relates to a press-formed product, and in particular, to a press-formed product including a top panel portion and a side panel portion.
2. Description of the Related Art
There are known press-formed products (press products), such as roof side rail reinforcements, that have a substantially hat-shaped cross-section or a substantially U-shaped cross sectional shape in the longitudinal direction and in which a side wall portion (side panel portion) of the cross section is curved (a bent portion is curved) in the longitudinal direction.
In some existing press-formed products, a side wall portion includes a length difference absorbing portion that is bent or curved in the thickness direction of the side wall portion so as to prevent or suppress torsion of the press-formed products due to occurrence of a stress difference caused by a length difference or the like (see, for example, Japanese Unexamined Patent Application Publication No. 2009-73420).
Springback and torsion due to springback usually occur in curved press-formed products.
That is, in a press-formed product 300 illustrated in FIGS. 18 to 19C, whose cross section (taken along a plane perpendicular to the longitudinal direction) is U-shaped and whose bent portion is curved, springback occurs as illustrated in FIGS. 20A to 20C. As a result, large torsion occurs in the press-formed product 300.
The term “REFERENCE” in FIGS. 20B and 20C refers to the target shape of the press-formed product (when manufacturing the press-formed product). The symbol “+” shows that springback is oriented outward from the cross section, and the symbol “−” shows that springback is oriented inward of the cross section (the same applies to FIGS. 3B, 3C, 11B, 11C, 14B, 14C, 17B, and 17C).
Occurrence of torsion can be prevented or suppressed by providing a side wall portion with a length difference absorbing portion that is bent or curved in the thickness direction of the side wall portion as in the related-art example described above. In this case, however, a problem arises in that the strength of the press-formed product is reduced because a bending line of the length difference absorbing portion becomes the origin of deformation of the press-formed product.
For example, as illustrated in FIGS. b 3 and 8 of Japanese Unexamined Patent Application Publication No. 2009-73420, the press-formed product includes bent portions (steps) 44 and 46. If a pressing load is applied to the press-formed product in the horizontal direction of FIG. 3 of Japanese Unexamined Patent Application Publication No. 2009-73420 (in the vertical direction of FIG. 8 of Japanese Unexamined Patent Application Publication No. 2009-73420), a bending moment is generated at the steps 44 and 46, and the strength of the press-formed product is reduced.